1. Field of the Invention
The invention relates to an apparatus for sorting metal bars or other elongate articles by length.
2. Description of the Prior Art
An apparatus for sorting by length is known in the metallurgical industry where it is used for example for the sorting by length of reinforcing bars or concrete-reinforcing bars. One such apparatus, made by the firm Morgardshammer, will now be described. In the manufacture of concrete-reinforcing bars a billet of steel is rolled out into a bar from which a number of concrete-reinforcing bars of a desired length are obtained by cutting. In general the length of a billet rolled out into a bar is not a whole number multiple of the desired length of a bar so that a shorter residual part bar is produced. After the cutting station, the bars of desired length and the residual part bar come to the sorting apparatus and are laid on a lateral transfer device against a stop with their rearmost ends next to each other.
Of the bars of the desired length the other, foremost ends are also adjacent; the foremost end of the residual part bar lies longitudinally between the two ends of a bar of desired length.
The bars lying next to one another moved laterally towards a pick-up device and a conveyor which can move the bars both laterally and longitudinally. The foremost end of each bar of desired length extends far enough forward to be picked up by the pick-up device. The pick-up device is be provided with a chain which runs across a bridge which extends laterally over the conveyor. A carrier plate joined to the chain picks up the foremost end of a bar and conveys this laterally across the conveyor. This means that the carrier plate blocks the bar from moving longitudinally. The conveyor itself conveys the other part of the bar laterally.
In this way the apparatus conveys a bar of desired length laterally across the conveyor. Bars selected in this way are then packed into bundles and taken away.
The foremost end of a residual part bar does not extend to the pick-up device and so is not picked up by a carrier plate of the chain and is not prevented from moving in longitudinal direction when it reaches the conveyor. The conveyor conveys the residual part bar longitudinally forwards beneath the bridge extending over the conveyor. Simultaneously the conveyor moves the residual part bar laterally. As a result of these two movements the residual part bar is conveyed obliquely across the conveyor and is set down next to the conveyor but separated from the barss of desired length. The residual part bars are then carried off separately for further processing.
In this known apparatus the conveyor has rollers having grooves extending helically and alongside each other. The axis of rotation of each grooved roller extends in the lateral direction of the conveyor. The width of a groove is here equal to its pitch. A bar of desired length, of which an end part is picked up by the pick-up device and of which a part of the length rests on the grooved rollers, is blocked longitudinally by the pick-up device and conveyed in lateral direction by the flanks of the groove in which it is lying.
The entire length of a residual part bar rests on the conveyor and is not prevented from longitudinal movement. The grooved rollers convey the residual part bar longitudinally at a speed approximately corresponding to the peripheral velocity of the grooved roller and laterally at a speed which depends on the pitch of the helical grooves.
A drawback of the apparatus described above is that the sorting capacity of the apparatus and at the same time, therefore, the processing capacity of an entire rolling mill, is dependent on the cross-sectional size of the concrete reinforcing bar and is less for smaller cross-sections.
As described above, the manufacture of concrete-reinforcing bars starts from a billet which in principle is of fixed section and length, irrespective of the section of the bars to be manufactured from it. When billets of equal weight are rolled out into smaller section bars, the total length of bar produced is greater. After cutting of a rolled billet into bars of desired constant length, a billet rolled out further also produces more bars of that length. However, each groove in a grooved roller may hold only one bar, so that when the section of the bar is smaller, although per unit time an equal total length is sorted, per unit time a smaller total weight of bars is sorted. As a result of this only a smaller total weight of billets can be rolled out.
One reason why each groove in a grooved roller holds only one bar is as follows. If there is more than one bar in a groove, friction between the concrete bars may prevent a residual part bar from being conveyed in sufficient longitudinal direction, when the residual part bar is lying against a bar of desired length which is being blocked from longitudinal movement by the pick-up device. In particular with ribbed concrete-reinforcing bars, friction between bars can be very high.
Changing the grooved rollers of the conveyor in dependence on the section of the bars is not a practical solution. A conventional conveyor has about 40 grooved rollers in total. Changing and aligning such a large number of grooved rollers takes too much time.
Measured in weight sorted, the capacity of an apparatus for sorting by length provided with grooved rollers is for a diameter of the bars of 16 mm approximately 16% and for a diameter of the bars of 12 mm approximately 10%, when the sorting capacity for a diameter of the bars of 40 mm is taken as 100%.
Another drawback of an apparatus with a conveyor provided with grooved rollers is the high wear of the grooves. The lateral movement of bars on the conveyor is produced because a leading blank of a groove exerts a lateral force on a bar. It is always the same leading flank of a groove which exerts the lateral force; only the position on the leading flank is dependent on process parameters and diameter of the bar. As a result of this, locally high wear of this leading flank of the groove occurs. The other leading flank of the groove and the base of the groove play a subsidiary role in both the lateral transfer and the longitudinal transfer and scarcely wear.
A grooved roller of which a flank is worn must be filled in, re-ground or replaced. The additional drawback attached to this is that an apparatus with a conveyor provided with grooved rollers is costly to purchase and maintain.
Another drawback of an apparatus with a conveyor provided with grooved rollers is that the pitch fixes the relationship between lateral velocity and longitudinal velocity of a bar being conveyed. The peripheral velocity of the grooved rollers is bound by a practical maximum. The product of pitch and peripheral velocity defines the sorting capacity of the installation. Therefore, the fixed relationship between pitch and peripheral velocity sets a practical limit on the sorting capacity. At the same time, once the pitch of the grooves has been selected, it is no longer possible to influence the position where a residual part bar is set down. Also where grooved rollers are not ideally aligned together extra friction occurs with associated extra wear.
NL-A-88-00425 (GB-A-117364) shows a sorter for metal bars in which the bars are conveyed laterally by a conveyor. Bars having a predetermined minimum length are picked up at their ends and lifted by a worm onto a second lateral conveyor. Bars of lesser length are not picked up and do not reach the second conveyor, but fall down to be transported away.